"We'll mix and match it," Yost said prior to the game. "We'll see where the lineup is. If the middle of the lineup is in the seventh inning, we'll use Kel there."
Soria, who signed a three-year, $25 million deal in the offseason, hasn't been hit hard. But he has walked five hitters in eight appearances and given up several seeing-eye hits.
Soria's entered Wednesday with a 7.71 ERA, and after he loaded the bases on Tuesday by giving up two singles and a walk, Yost removed him in the eighth inning of the Royals' 8-6 win. Soria was booed at Kauffman Stadium.
On Wednesday, Yost, Soria and pitching coach Dave Eiland pored over video and spotted a flaw in Soria's mechanics.
"We've been over video, and it's just a little mechanical thing with his front side that Dave sees," Yost said. "Jack can fix it.
"The thing about Jack is that when he's right, it's about a 10-12 pitch inning. Boom, boom, boom. But his mechanics are off and everything is tailing off arm side.
"Hopefully it is an easy, quick fix. It's not a major overhaul."
Yost said he and his staff have not lost faith in Soria, and the righty will remain a valuable asset among the Royals' big four relievers -- Herrera, Luke Hochevar, Soria and closer Wade Davis.
"Everybody had a great spring," Yost said. "Soria had a great spring. Hoch had a great spring. Kel had a great spring. And Wade is Wade. We started the season with a plan to set up everyone in a spot they'd know.
"But now, two weeks into the season, you start to see who is hot and who is not. Then you start mixing and matching. Pitchers, like hitters, will go through a little bit of a slump. And you make adjustments. You just match up from the sixth inning on."
Yost said he isn't paying attention to some fans' panic over Soria.
"We know Jack has been pitching into some bad luck -- ground balls that are getting through," Yost said before Soria's outing Wednesday. "They're not ripping the walls off against him.
"He's really close to reeling off about 20 consecutive appearances without a run."